Wednesday, May 21, 2008

Avian influenza has spread and, while it has not reached pandemic proportions, constant vigilance is still crucial.

Avian flu is in the news so much nowadays that some of us may have become desensitised to the urgency of the matter.

When news about avian flu first broke in 1997, there was much concern when it revealed that the virus, having transmitted from chickens to humans, had infected 18 people and killed six. Then, things quieted down for a few years, until 2003 when avian flu made an appearance again and never went away.A health worker injecting a chicken with the bird flu vaccine in a poultry farm in China. The H5N1 (virus) may never become pandemic but, if it does, the catastrophic situation could be more than we can even imagine.

According to Prof Malik Peiris, the avian flu problem has been progressively increasing. Peiris is the virologist who discovered the aetiological agent that causes Severe Acute Respiratory Syndrome (SARS), and has been involved with avian flu research. He is based in Hong Kong, but was in Kuala Lumpur recently to receive the Mahathir Science Award 2007, Malaysia’s most prestigious science award named in honour of former prime minister Tun Dr Mahathir Mohamad.

During the SARS outbreak, Peiris led a team of researchers from the University of Hong Kong and Queen Mary’s Hospital who managed to identify the SARS coronavirus within weeks. That breakthrough, along with other measures, led to the successful control and containment of the outbreak.

After the avian flu outbreak in 1997, Peiris subsequently became more interested in avian and animal influenza viruses and their danger to humans.

“If you look at the geographical area that is affected, it is now bigger than it was two or three years ago,” said Peiris. “So if you look at that scale, at the poultry level, it is increasing. It is certainly not going to disappear. This is going to be entrenched, and we are not going to be able to get rid of it in the short term.”

Fortunately for us, the efficiency of the virus infecting humans is still very low. Most of the time, people who are exposed to the virus are not infected. But Peiris identifies two levels to the problem. First, the huge poultry industry would mean that people’s livelihood, the country’s economy and human health would be affected. Second, the occasional transmission of the virus from poultry to humans, where the real danger is, if the transmissions are not monitored and controlled, and the virus is allowed to adapt and transfer between humans.

“There are people who say, well, this virus has been here for 10 years, and it has not really done this, so it won’t happen,” said Peiris. “I think that is extremely dangerous. That was exactly the same situation with SARS. That virus was also probably in the animal reservoir for quite a long time.”Prof Malik Peiris: ‘We really have to take it (bird flu) seriously, and take measures to see what can be done.’

But Peiris pointed out that this doesn’t mean we should start panicking, nor should we be complacent about it.

“On a risk-assessment basis, the H5N1 (virus) may never become pandemic,” said Peiris. “But the point is, if it does, the catastrophic situation could be more than we can even imagine. It definitely could be much worse than any of the past pandemics. We really have to take it seriously, and take measures to see what can be done.”

Mutation

While there are claims that the virus is two mutations away from human-to-human transmission, and that it has learnt to infect humans more easily, Peiris dismissed these as “simplistic”.

“It obviously requires a lot of adaptations, not just one or two,” Peiris explained. “A number of studies have shown that mixing the genes alone doesn’t do it. It requires a multi-step process. That’s probably why it hasn’t happened so far. But I think these rare events do happen, and we’d be very stupid not to take precautions.”

Peiris warned that the problem is currently “grossly underestimated”. In countries where the virus is endemic, he said, much more poultry carry the virus than people imagine. Poultry enter the markets and are slaughtered, so it doesn’t seem as though they are dying from the virus. But the virus continues to circulate as farmers bring their cages to the markets, leave the poultry there, and return to their farms with the cages, unaware that those cages may have come into contact with the virus.

“Once the virus gets in a market, it remains there almost forever,” said Peiris.

He said countries such as Malaysia, Japan, North Korea and India have been successful in detecting the virus early and eradicating it, demonstrating the need to be alert at all times.

Even during the lull between 1997 and 2003, virologists and researchers continued their surveillance and published papers on their findings, all the while aware that the virus was still lurking somewhere and was adapting.

Defence

While the capacity for producing vaccines has increased, Peiris said the real challenge is in creating a vaccine that would protect against more than one strain of the H5 virus which is now diverse. The fact that we do not know which strain will become pandemic means there needs to be broad protection. Peiris said the newer vaccines that have come to clinical trials look promising, but there is also the problem of trying to produce enough in an emergency.

This raises some tricky issues. We could wait for a pandemic before producing the vaccine, but chances are there would not be enough time because it takes months to scale up production. The second option, said Peiris, is to stockpile the vaccine in advance, but money could be wasted if a pandemic never happens.

This would mean that an ideal situation where one could walk into a store and purchase the vaccine in an emergency would never be viable.

“You can’t have a vaccine that is not regularly used sitting in the stores,” said Peiris. “For the next five years, it might not be used, and it will be out of date. I think the real possibility is to stockpile it in bulk at governmental level. So if the emergency comes, it can be quickly distributed.”

Asked if there is a beacon of light in this seemingly hopeless situation, Peiris pointed to how SARS was successfully controlled, and that it was a great achievement of global collaboration.

“I think the control of SARS was probably one of the greatest triumphs for global public health,” he said. “So things can be done, for sure. But we can’t sit back and assume that things will happen. It is actually planning, intervention, collaboration and all these things that made it happen.”

1 Comments:

Proved awareness to ecology and transmission is necessary to understand the spread of avian flu. For this it is insufficient exclusive to test samples from wild birds, poultry and humans for avian flu viruses. Samples from the known abiotic vehicles also have to be analysed. There are plain links between the cold, rainy seasons as well as floods and the spread of avian flu. That is just why abiotic vehicles have to be analysed. The direct biotic transmission from birds, poultry or humans to humans can not depend on the cold, rainy seasons or floods. Water is a very efficient abiotic vehicle for the spread of viruses - in particular of fecal as well as by mouth, nose and eyes excreted viruses.

Infected birds and poultry can everywhere contaminate the drinking water. All humans have very intensive contact to drinking water. Spread of avian flu by drinking water can explain small clusters in households too. Proving viruses in water is difficult because of dilution. If you find no viruses you can not be sure that there are not any. On the other hand in water viruses remain viable for a long time. Water has to be tested for influenza viruses by cell culture and in particular by the more sensitive molecular biology method PCR.

There is a widespread link between avian flu and water, e.g. in Egypt to the Nile delta or Indonesia to residential districts of less prosperous humans with backyard flocks and without central water supply as in Vietnam: http://www.cdc.gov/ncidod/EID/vol12no12/06-0829.htm. See also the WHO web side: http://www.who.int/water_sanitation_health/emerging/h5n1background.pdf .

Transmission of avian flu by direct contact to infected poultry is an unproved assumption from the WHO. There is no evidence that influenza primarily is transmitted by saliva droplets: “Transmission of influenza A in human beings” http://www.thelancet.com/journals/laninf/article/PIIS1473309907700294/abstract?iseop=true .

Avian flu infections may increase in consequence to increase of virus circulation. In hot climates/the tropics flood-related influenza is typical after extreme weather and floods. Virulence of influenza viruses depends on temperature and time. Special in cases of local water supplies with “young” and fresh H5N1 contaminated water from low local wells, cisterns, tanks, rain barrels, ponds, rivers or rice paddies this pathway can explain small clusters in households. At 24°C e.g. in the tropics the virulence of influenza viruses in water amount to 2 days. In temperate climates for “older” water from central water supplies cold water is decisive to virulence of viruses. At 7°C the virulence of influenza viruses in water amount to 14 days.

Human to human and contact transmission of influenza occur - but are overvalued immense. In the course of influenza epidemics in Germany, recognized clusters are rare, accounting for just 9 percent of cases e.g. in the 2005 season. In temperate climates the lethal H5N1 virus will be transferred to humans via cold drinking water, as with the birds in February and March 2006, strong seasonal at the time when drinking water has its temperature minimum.

The performance to eliminate viruses from the drinking water processing plants regularly does not meet the requirements of the WHO and the USA/USEPA. Conventional disinfection procedures are poor, because microorganisms in the water are not in suspension, but embedded in particles. Even ground water used for drinking water is not free from viruses.

http://www.un.org/apps/news/story.asp?NewsID=26096&Cr=&Cr1 Ducks and rice [paddies = flooded by water] major factors in bird flu outbreaks, says UN agencyDucks and rice fields may be a critical factor in spreading H5N1 26 March 2008 – Ducks, rice [fields, paddies = flooded by water! Farmers on work drink the water from rice paddies!] and people – and not chickens – have emerged as the most significant factors in the spread of avian influenza in Thailand and Viet Nam, according to a study carried out by a group of experts from the United Nations Food and Agriculture Organization (FAO) and associated research centres.

“Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia: ducks, rice and people” also finds that these factors are probably behind persistent outbreaks in other countries such as Cambodia and Laos. The study, which examined a series of waves of H5N1 highly pathogenic avian influenza in Thailand and Viet Nam between early 2004 and late 2005, was initiated and coordinated by FAO senior veterinary officer Jan Slingenbergh and just published in the latest issue of the Proceedings of the National Academy of Sciences of the United States. Through the use of satellite mapping, researchers looked at a number of different factors, including the numbers of ducks, geese and chickens, human population size, rice cultivation and geography, and found a strong link between duck grazing patterns and rice cropping intensity.

In Thailand, for example, the proportion of young ducks in flocks was found to peak in September-October; these rapidly growing young ducks can therefore benefit from the peak of the rice harvest in November-December [at the beginning of the cold: Thailand, Viet Nam, Cambodia, Laos are situated – different from Indonesia – in the northern hemisphere].

“These peaks in congregation of ducks indicate periods in which there is an increase in the chances for virus release and exposure, and rice paddies often become a temporary habitat for wild bird species,” the agency said in a news release.

“We now know much better where and when to expect H5N1 flare-ups, and this helps to target prevention and control,” said Mr. Slingenbergh. “In addition, with virus persistence becoming increasingly confined to areas with intensive rice-duck agriculture in eastern and south-eastern Asia, evolution of the H5N1 virus may become easier to predict.”

He said the findings can help better target control efforts and replace indiscriminate mass vaccination. FAO estimates that approximately 90 per cent of the world’s more than 1 billion domestic ducks are in Asia, with about 75 per cent of that in China and Viet Nam. Thailand has about 11 million ducks.